The invention relates to knee joint prostheses and more particularly to tibial components of knee joint prostheses that feature a tibial bearing insert that is rotatable with respect to a tibial tray upon which it is mounted.
Joint replacement surgery is quite common and enables many individuals to function normally when otherwise it would not be possible to do so. Artificial joints are normally composed of metallic, ceramic and/or plastic components that are fixed to existing bone.
Knee arthoplasty is a well known surgical procedure by which a diseased and/or damaged natural knee joint is replaced with a prosthetic knee joint. Typical knee protheses include a femoral component, a patella component, a tibial tray or plateau, and a tibial bearing insert. The femoral component generally includes a pair of laterally spaced apart condylar portions, the distal surfaces of which articulate with complementary condylar elements formed in a tibial bearing insert.
The tibial tray is mounted within the tibia of a patient. Typically, the tibial bearing insert, which is usually made of ultra high molecular weight polyethylene (UHMWPE) is mounted upon the superior surface of the tibial tray. Load and stress are placed upon the knee prosthesis, and particularly on the tibial bearing insert, during normal daily use. These forces may lead to the displacement or dislocation of the insert from the tibial tray. To accommodate these forces, and to reduce the chances for dislocation, some tibial components of knee prostheses have been designed to allow rotation of the tibial bearing insert relative to the proximal or superior surface of the tibial tray, about the longitudinal axis of the prosthesis. Such rotation, when controlled, can increase the contact area between the femoral condyles and the tibial bearing insert throughout the range of knee motion, thus reducing stress on the tibial bearing insert.
Some knee prosthesis tibial components accommodate insert rotation without providing axial securement of the tibial bearing insert within the tibial tray. That is, some tibial bearing inserts that are able to rotate with respect to a tibial tray are not fully secured within the tibial tray. Certain forces to which the knee is subjected, particularly forces with axially directed components, may cause the tibial bearing insert to separate from the tibial tray.
Various designs for rotatable tibial components of knee joint prostheses are known in the art. For example, U.S. Pat. No. 4,219,893 (Noiles) and U.S. Pat. No. 4,301,553 (Noiles) disclose knee joint prostheses in which the tibial component comprises a tibial tray having a bearing surface with a recessed region within which the tibial bearing insert may rest. A sufficient clearance is provided in the bearing surface of the tibial tray to allow some medial-lateral rotation of the tibial bearing insert with respect to the tray. Other patents that disclose tibial components of knee joint prostheses in which a tibial bearing insert is rotatable with respect to the tibial tray are disclosed in U.S. Pat. Nos. 5,059,216 (Winters); 5,071,438 (Jones et al); 5,171,283 (Pappas et al); and 5,489,311 (Cipolletti).
Despite the existing designs for knee joint prostheses having a rotatable tibial component, there remains a need for prostheses that allow rotation of the tibial bearing insert to accommodate the stresses placed upon the knee. At the same time, such tibial bearing inserts should possess sufficient axial securement so as to decrease or eliminate the possibility of subluxation of the tibial bearing insert.